DrL is a force-directed graph layout toolbox focused on real-world large= -scale graphs (see References). This toolbox includes:

=20- =20
- Standard force-directed layout of graphs using algorithm based on the p= opular VxOrd routine (used in the VxInsight program). =20
- Parallel version of force-directed layout algorithm. =20
- Recursive multilevel version for obtaining better layouts of very large= graphs. =20
- Ability to add new vertices to a previously drawn graph. =20

DrL has been used on graphs up to 2 million vertices. It is written in C= ++ and can be used with Linux, Windows, and Mac.

=20- =20
- Source Code: http://www.cs.sandia.gov/~smartin= /DrL.tar.gz =20
- Binaries: link =20
- Home Page: http://www.cs.sandia.gov/~smarti= n/software.html =20

DrL is one of the few force-directed layout algorithms that can scale to= over 1 million nodes, making it ideal for large graphs. However, small gra= phs (hundreds or less) do not always end up looking so good. This algorithm= expects similarity networks, so some networks may need to derive another n= etwork with weighted edges declaring the similarity between nodes.

=20The version of DrL included in NWB only does the standard force-directed= layout (no recursive or parallel version).

=20Force-directed layout of large networks.

=20DrL expects the edges to be weighted, directed edges where the weight (g= reater than zero) denotes how similar the two nodes are (higher is more sim= ilar). The NWB version has several parameters. The edge cutting parameter e= xpresses how much automatic edge cutting should be done. 0 means as little = as possible, 1 as much as possible. Around .8 is a good value to use. The w= eight attribute parameter lets you choose which edge attribute in the netwo= rk corresponds to the similarity weight. The X and Y parameters let you cho= ose the attribute names to be used in the returned network which correspond= s to the X and Y coordinates computed by the layout algorithm for the nodes= .

=20- =20
- For article/citation networks, feed the network into either cocitation = or bibliographic coupling for computing similarity. Use this network for la= ying out DrL. =20
- GUESS or Pre-Defined Layout can be used to see the layout created by Dr= L. =20

To see the VxOrd/DrL layout in GUESS, you must run the following command= in the GUESS interpreter (click the 'Interpreter' tab near the bottom of t= he GUESS interface):

=20=20

for n in g.nodes: n.x =3D n.xpos * 100 n.y =3D n.ypos * 100=20

(Whitespace is significant.)

=20This assumes you used the default 'xpos' and 'ypos' labels suggested by = the DrL algorithm.

=20This code is translated into English as the following: For every node in= the network,

=20=20

make the GUESS x coordinate equal to the DrL-generated X coordinate tim= es 100 make the GUESS y coordinate equal to the DrL-generated Y coordinate tim= es 100=20

We multiply by 100 because DrL coordinates are on a smaller scale than G= UESS coordinates, so we need to enlarge the DrL coordinates to see the netw= ork structure (otherwise it will appear that the nodes are nearly on top of= each other).

=20- =20
- Now you can switch between the GUESS layout options to retrieve differe= nt visualization effects. Recommended: Switch between Bin Pack and GEM a fe= w times. =20

DrL was created at Sandia National Labs

=20- =20
- S. Martin, W. M. Brown, K. Boyack, "DrL: Distributed Recursive (Graph) = Layout," in prepartion for Journal of Graph Algorithms and Applications.=20
- Davidson, G.S., Wylie, B.N. & Boyack, = K.W. (2001). Cluster stability and the use of noise in interpretation of cl= ustering. Accepted by IEEE Information Visualization `01. =20

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